// SPDX-License-Identifier: GPL-2.0
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/*
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* Auto-group scheduling implementation:
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*/
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#include <linux/nospec.h>
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#include "sched.h"
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unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
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static struct autogroup autogroup_default;
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static atomic_t autogroup_seq_nr;
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void __init autogroup_init(struct task_struct *init_task)
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{
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autogroup_default.tg = &root_task_group;
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kref_init(&autogroup_default.kref);
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init_rwsem(&autogroup_default.lock);
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init_task->signal->autogroup = &autogroup_default;
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}
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void autogroup_free(struct task_group *tg)
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{
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kfree(tg->autogroup);
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}
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static inline void autogroup_destroy(struct kref *kref)
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{
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struct autogroup *ag = container_of(kref, struct autogroup, kref);
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#ifdef CONFIG_RT_GROUP_SCHED
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/* We've redirected RT tasks to the root task group... */
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ag->tg->rt_se = NULL;
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ag->tg->rt_rq = NULL;
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#endif
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sched_offline_group(ag->tg);
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sched_destroy_group(ag->tg);
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}
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static inline void autogroup_kref_put(struct autogroup *ag)
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{
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kref_put(&ag->kref, autogroup_destroy);
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}
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static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
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{
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kref_get(&ag->kref);
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return ag;
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}
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static inline struct autogroup *autogroup_task_get(struct task_struct *p)
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{
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struct autogroup *ag;
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unsigned long flags;
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if (!lock_task_sighand(p, &flags))
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return autogroup_kref_get(&autogroup_default);
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ag = autogroup_kref_get(p->signal->autogroup);
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unlock_task_sighand(p, &flags);
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return ag;
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}
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static inline struct autogroup *autogroup_create(void)
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{
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struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL);
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struct task_group *tg;
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if (!ag)
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goto out_fail;
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tg = sched_create_group(&root_task_group);
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if (IS_ERR(tg))
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goto out_free;
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kref_init(&ag->kref);
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init_rwsem(&ag->lock);
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ag->id = atomic_inc_return(&autogroup_seq_nr);
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ag->tg = tg;
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#ifdef CONFIG_RT_GROUP_SCHED
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/*
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* Autogroup RT tasks are redirected to the root task group
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* so we don't have to move tasks around upon policy change,
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* or flail around trying to allocate bandwidth on the fly.
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* A bandwidth exception in __sched_setscheduler() allows
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* the policy change to proceed.
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*/
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free_rt_sched_group(tg);
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tg->rt_se = root_task_group.rt_se;
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tg->rt_rq = root_task_group.rt_rq;
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#endif
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tg->autogroup = ag;
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sched_online_group(tg, &root_task_group);
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return ag;
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out_free:
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kfree(ag);
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out_fail:
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if (printk_ratelimit()) {
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printk(KERN_WARNING "autogroup_create: %s failure.\n",
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ag ? "sched_create_group()" : "kzalloc()");
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}
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return autogroup_kref_get(&autogroup_default);
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}
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bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
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{
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if (tg != &root_task_group)
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return false;
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/*
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* If we race with autogroup_move_group() the caller can use the old
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* value of signal->autogroup but in this case sched_move_task() will
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* be called again before autogroup_kref_put().
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*
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* However, there is no way sched_autogroup_exit_task() could tell us
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* to avoid autogroup->tg, so we abuse PF_EXITING flag for this case.
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*/
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if (p->flags & PF_EXITING)
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return false;
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return true;
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}
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void sched_autogroup_exit_task(struct task_struct *p)
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{
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/*
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* We are going to call exit_notify() and autogroup_move_group() can't
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* see this thread after that: we can no longer use signal->autogroup.
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* See the PF_EXITING check in task_wants_autogroup().
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*/
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sched_move_task(p);
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}
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static void
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autogroup_move_group(struct task_struct *p, struct autogroup *ag)
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{
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struct autogroup *prev;
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struct task_struct *t;
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unsigned long flags;
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BUG_ON(!lock_task_sighand(p, &flags));
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prev = p->signal->autogroup;
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if (prev == ag) {
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unlock_task_sighand(p, &flags);
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return;
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}
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p->signal->autogroup = autogroup_kref_get(ag);
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/*
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* We can't avoid sched_move_task() after we changed signal->autogroup,
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* this process can already run with task_group() == prev->tg or we can
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* race with cgroup code which can read autogroup = prev under rq->lock.
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* In the latter case for_each_thread() can not miss a migrating thread,
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* cpu_cgroup_attach() must not be possible after cgroup_exit() and it
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* can't be removed from thread list, we hold ->siglock.
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*
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* If an exiting thread was already removed from thread list we rely on
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* sched_autogroup_exit_task().
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*/
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for_each_thread(p, t)
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sched_move_task(t);
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unlock_task_sighand(p, &flags);
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autogroup_kref_put(prev);
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}
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/* Allocates GFP_KERNEL, cannot be called under any spinlock: */
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void sched_autogroup_create_attach(struct task_struct *p)
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{
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struct autogroup *ag = autogroup_create();
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autogroup_move_group(p, ag);
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/* Drop extra reference added by autogroup_create(): */
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autogroup_kref_put(ag);
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}
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EXPORT_SYMBOL(sched_autogroup_create_attach);
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/* Cannot be called under siglock. Currently has no users: */
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void sched_autogroup_detach(struct task_struct *p)
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{
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autogroup_move_group(p, &autogroup_default);
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}
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EXPORT_SYMBOL(sched_autogroup_detach);
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void sched_autogroup_fork(struct signal_struct *sig)
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{
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sig->autogroup = autogroup_task_get(current);
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}
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void sched_autogroup_exit(struct signal_struct *sig)
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{
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autogroup_kref_put(sig->autogroup);
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}
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static int __init setup_autogroup(char *str)
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{
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sysctl_sched_autogroup_enabled = 0;
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return 1;
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}
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__setup("noautogroup", setup_autogroup);
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#ifdef CONFIG_PROC_FS
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int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
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{
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static unsigned long next = INITIAL_JIFFIES;
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struct autogroup *ag;
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unsigned long shares;
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int err, idx;
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if (nice < MIN_NICE || nice > MAX_NICE)
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return -EINVAL;
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err = security_task_setnice(current, nice);
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if (err)
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return err;
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if (nice < 0 && !can_nice(current, nice))
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return -EPERM;
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/* This is a heavy operation, taking global locks.. */
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if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
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return -EAGAIN;
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next = HZ / 10 + jiffies;
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ag = autogroup_task_get(p);
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idx = array_index_nospec(nice + 20, 40);
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shares = scale_load(sched_prio_to_weight[idx]);
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down_write(&ag->lock);
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err = sched_group_set_shares(ag->tg, shares);
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if (!err)
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ag->nice = nice;
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up_write(&ag->lock);
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autogroup_kref_put(ag);
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return err;
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}
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void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
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{
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struct autogroup *ag = autogroup_task_get(p);
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if (!task_group_is_autogroup(ag->tg))
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goto out;
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down_read(&ag->lock);
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seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
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up_read(&ag->lock);
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out:
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autogroup_kref_put(ag);
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}
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#endif /* CONFIG_PROC_FS */
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int autogroup_path(struct task_group *tg, char *buf, int buflen)
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{
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if (!task_group_is_autogroup(tg))
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return 0;
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return snprintf(buf, buflen, "%s-%ld", "/autogroup", tg->autogroup->id);
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}
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